Thermal retransfer printing involves forming an image (in reverse) on a retransfer intermediate sheet using one or more thermally transferable dyes. The image is then thermally transferred to a surface of an article by bringing the image into contact with the article surface and applying heat.
Conventional infrared heating sources suffer from a number of issues. The retransfer intermediate sheet is typically preheated to be easily applied to and conform to the contours of an article. In order to achieve uniform heating of the sheet, it must be positioned equidistant from the infrared heating source. Since it is difficult to optimize the equidistant position of the retransfer sheet when using infrared heating sources, the retransfer sheet is sometimes too soft to properly conform to the contours of three dimensional (3D) articles and sometimes too hard to be appropriately applied on the surface of 3D articles. In addition, the radiation of the infrared heating source might be so intense that the retransfer intermediate sheet could be deformed due to the intense radiation.
In addition, since the conventional infrared heating source can reach its predetermined temperature quickly, the acute radiation from the infrared heating source might damage certain fragile articles. However, if the predetermined temperature setting is reduced, the thermal transfer process will be too slow for economical production.
Moreover, the infrared heating source is not optimized for 3D articles that have upwardly projecting portions, as side or lower surfaces of the articles tend to remain cooler than upper surfaces. This results in uneven heating of 3D articles and the sheet and consequent variable dye transfer, with potentially poor dye transfer occurring on cooler regions of an article. This can result in poor overall print quality.